The Barcelona midfielder turned in an impressive display in La Roja's 1-1 draw against Italy on Sunday and was one of the biggest threats to Gianluigi Buffon's goal throughout the contest.
Croatia, who defeated Republic of Ireland 3-1 in their Euro 2012 opener, will tackle Spain in their last group match, in which Modric will come face-to-face with Iniesta.
The Tottenham star warned Vincent del Bosque's team not to underestimate his side's chances of upsetting the European and world champions, however.
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"Spain are the best team in the world. It will be a very hard match, but we can beat anyone if we play like we did against Ireland.
"Their match against Italy? I was surprised that they started without a striker."
Croatia will attempt to defend their place at the summit of Group C when they take on Italy on Thursday before they clash with Spain in a week's time.